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Types of Reactions
Oxidation Reduction Double Replacement
Synthesis (Combination) Precipitation
Decomposition Neutralization (Acid/Base)
Combustion
Single Replacement
Redox Reactions (Oxidation Reduction Reactions) – transfer of electrons
Oxidation numbers help us determine what is being reduced versus oxidized. See bonding and nomenclature notes for rules on assigning oxidation numbers.
Oxidation is losing electrons (OIL)
Reduction is gaining electrons (RIG)
Oxidation and Reduction always occurs in pairs. You cannot have one without the other.
EX 1. 2Na + Cl 2 2NaCl (SYNTHESIS)
Metals lose electrons to become cations and therefore are oxidized
Na Na+^ + e-^ sodium was oxidized. Lost one electron.
Nonmetals gain electrons to become anions and therefore are reduced.
Cl + e-^ Cl-^ chlorine was reduced. Each chlorine gains one electron becomes chlor ide.
EX 2. Calcium atoms react with oxygen gas to form a compound.
2Ca (^) (s) + O 2 (g) 2CaO (^) (s) (SYNTHESIS)
metal + nonmetal ionic compound (you know how to write these formulas!)
Write the half reactions. (Identify what is oxidized versus what is reduced.)
Ca Ca2+^ + 2e-^ calcium is oxidized.
O + 2e-^ O2-^ oxygen is reduced.
EX 3. 6Na + Fe 2 O 3 3Na 2 O + 2Fe (SINGLE REPLACEMENT)
Write the half reactions. (Identify what is oxidized versus what is reduced.)
Na Na+^ + e-^ sodium is oxidized.
Fe3+^ + 3e-^ Fe iron (III) ion is reduced.
Electrons are transferred from the sodium atom to Fe3+.
EX 4. 2Cs + F 2 2CsF (SYNTHESIS)
Cs Cs+^ + e-^ Cesium is oxidized.
F + e-^ F-^ Fluorine is reduced and becomes fluor ide.
EX 5. 2Al + 3ZnO Al 2 O 3 + 3Zn (SINGLE REPLACEMENT)
Al Al3+^ + 3e-^ Aluminum is oxidized
Zn2+^ + 2e-^ Zn Zinc ion is reduced.
EX 6. 2 NaI + F 2 2NaF + I 2 (SINGLE REPLACEMENT)
F + e-^ F-^ Fluorine is reduced and becomes fluor ide.
I-^ I + e-^ Iod ide is oxidized and becomes iod ine.
Synthesis – 2 or more substances combine to make a new compound. General form A + B AB A and B can be elements or compounds. AB is always a compound.
2 nonmetals from a molecular compound. (product is unpredictable) Ex. S + O 2 SO 2 Ex. 2S + 3O 2 SO 3
Metal and nonmetal from an ionic compound. If the metal is a Representative element then the product is predictable. If the metal is a Transition metal then the product is unpredictable. Ex. 2Na + Cl 2 2NaCl Ex. 2Cu + O 2 2CuO Ex. 4Cu + O 2 2Cu 2 O
Metal oxides react with water to form metal hydroxides (bases). Ex. Na 2 O + H 2 O 2NaOH
Nonmetal oxides react with water to form oxyacids. Ex. CO 2 + H 2 O H 2 CO 3
Consult an activity series to make sure reaction can take place. (Page 217 Table 8.2) activity – ability of an element to react. activity series – list of elements organized according to their reactivity. Being able to write a chemical equation does NOT mean it will occur.
EX. 2HBr + I 2 2HI + Br 2 Reaction does NOT occur!!
Double Replacement (Double Displacement) – exchange of positive ions between two ionic compounds general form: AB + CD AD + CB A & C are positive ions, A & C switch places B & D are negative ions
Ex. NaCl (^) (aq) + AgNO 3 (aq) AgCl (^) (s) + NaNO3 (aq) AgCl is a precipitate See Appendix A Reference page 7 Table A-7 for a Table of Solubility
3 general characteristics
- Formation of a precipitate
- Production of a gas
- Formation of a molecular compound
Neutralization (Acid/Base) – acid reacts with a base to form salt and water General form: HX + YOH HY + H 2 O HX is an acid and YOH is a base. X is a nonmetal or polyatomic anion and Y is a metal or the ammonium ion. HY is a salt (ionic compound)
Ex. HCl + KOH KCl + H 2 O
Net ionic equation – equation that indicates the particles that actually participate in the reaction
Spectator ions – ions that are not directly involved in the reaction
Molecular equation: Ex. NaCl (^) (aq) + AgNO 3 (aq) AgCl (^) (s) + NaNO 3 (aq)
Determine the spectator ions by separating ions that are in aqueous solutions (represent all reactants and products that are strong electrolytes as ions)
Complete ionic equation: Ex. Na+^ + Cl-^ + Ag+^ + NO 3 -^ AgCl (^) (s) + Na+^ + NO 3 -
Identify ions that remain unchanged i.e. show up on both sides of the equation (Spectator ions)
Spectator ions: Ex. Na+^ + NO 3 -
Rewrite equation without the spectator ions (Net ionic equation)
Net ionic equation: Ag+ (aq) + Cl- (aq) AgCl (^) (s)
